An Indonesian teenager has survived 49 days adrift at sea after the wooden fish trap he was employed to mind slipped its moorings.

Aldi Novel Adilang said he ran out of food within a week and survived on fish and seawater he strained through his clothing.

The 18-year-old added that he turned on a lamp every time he sighted a ship and cannot remember how many passed by “unaware of my ordeal”.

He was rescued by a Panamanian-flagged vessel off Guam on August 31, about 1,200 miles from his original location, and returned to Indonesia with officials earlier this month, according to the Indonesian consulate in Osaka, Japan.

The teenager had been employed since the age of 16 in one of the world’s loneliest jobs: lamp lighter on a rompong – a wooden fishing raft with a hut on top – moored about 78 miles (125km) off the coast of North Sulawesi.

The coastline is not visible from the fishing rafts and the numerous rompong are miles apart from one another, said Mr Adilang’s mother, Met Kahiking.

Supplies are dropped off to the light keepers about once a week.

“I was on the raft for one month and 18 days. My food ran out after the first week,” said Mr Adilang.

When it did not rain for days “I had to soak my clothes in the sea, then I squeezed and drank the water”, he said.

Aldi Novel Adilang sits on the deck of the MV Arpeggio after being rescued (Indonesian Consulate General in Osaka via AP)

The teenager’s father, Alfian Adilang, said the family is overjoyed at his return but angry with his employer.

The rafts are anchored with ropes and Mr Adilang said strong friction caused them to break.

“I thought I will never meet my parents again, so I just prayed every day,” he said.

The MV Arpeggio, which rescued Mr Adilang off Guam, contacted the Indonesian mission in Osaka when it docked and officials collected him on September 6, the Osaka consulate said in a statement.